94 zxr750 Won't rev

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94 zxr750 Won't rev

Postby willrcr15 » Sat May 11, 2013 6:12 pm

Hi all, I'm having trouble getting my zxr750 to rev past 4 - 5000 rpm.
I got her registered yesterday & at long last took it for a blast but no revs in fact she fouled plugs & wouldn't re start after I got home so I bought new plugs.
It seemed to be fixed with the new plugs but soon returned to crap.
I've tried everything except the thing that'll fix it.
Carbies are clean, new plugs, leads are good, caps are good, pump is good, new fuel filter.
She is smooth as silk out the drive & along the road until I open the throttle & it just chokes over 3000, seems like its starving for fuel. If I drag the choke open it responds & goes & will rev through to about 9000 rpm then acts up like you'd expect with the choke on, so it's not electrical.
The only thing Ive not checked is the float levels but they look pristine, stupid not to have checked them though, theyve been out 5 times.
I'll do it all over again & this time check them & spray the carb's out with cleaner but if anyone has had the same thing I'd love to hear about it.
Oh & if it makes any difference, she's got a Hindle full system & a K&N air filter.
Looking forward to the quiet life !
2 Honda NSR 150 SP's for the kids
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97 Suz GSXR750
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Re: 94 zxr750 Won't rev

Postby greenman43 » Sat May 11, 2013 10:05 pm

Battery charging ok ? Blocked fuel tank breather maybe ? Is it running stnadard jetting - might be a bit lean on top for the pipe & filter.

Cheers,
Brian
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Re: 94 zxr750 Won't rev

Postby ajverma » Sat May 11, 2013 10:16 pm

Hi Matey,

Check your carb vacuum lines and make sure they're completely clear, also check the vac line going to the airbox as mine was having the issues you're talking about and it turned out to be a mixture of a partially blocked vac line to the airbox and a half clogged fuel tap.

Floats could also be the problem and it could be feeding fuel straight down the intake even when the bike is off. Also check your throttle cable is free and you aren't unknowingly flooding the bike because of a sticky throttle.
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Re: 94 zxr750 Won't rev

Postby ajverma » Sat May 11, 2013 10:22 pm

Only other thing I can think of is that the bike might have flooded itself while sitting and once at operating temp it will run like sh*t and not rev/rev feeling like it is starving for fuel.

To be safe, check your oil level, and shake the bike a bit, if it seems too thin, replace the oil and take the new plugs out and let them dry, leave the plug holes open to the air overnight so the remaining fuel in the chamber can evaporate (if it's emulsified with the oil).


If the plugs are salvageable in the morning, put them in and see how she runs. It sounds so much like you're running a flooded bike.
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Re: 94 zxr750 Won't rev

Postby willrcr15 » Sun May 12, 2013 11:31 am

Thanks guy's,
Ive snuck in a session in the shed.
Checked the float levels & put a can of carby cleaner through & all is perfect.
Took her for a squirt & still the same.
The other thing Ive done is to block off & disconnect all the bullshit pollution gear, so she's running free of all the hoses & valves. All the air box holes are blocked of course. The only hose remaining is the engine crankcase breather & valve as it'll have no bearing on performance.
Also blocked off are the vacuum tubes on the inlet manifold for carby balancing & tuning.
Ive set the pilot needles at 2 & 1/4 out.
I'd be very surprised if the gets aren't standard & I think I checked once early on & remember they were, but were doing up 3 bikes & could be mixed up, I'm getting on.
It still responds to the choke when at about 5000 rpm & wants to go but struggles. I can feel the power & can't wait to feel it all on song, I'm used to old sluggish Ducati's with about 80 hp & this thing is an absolute missile & handles like a Bimota but I'm not game to put it into a corner hard in case she coughs mid corner.
You could be forgiven for thinking it's electrical as it feels like a breakdown under load but when she responds to some fuel from the choke it rules that out.
What are these vacuum tubes, obviously there to lift the needles, something I haven't studied now you mention it.
I did find, yesterday, that one of the slides wouldn't lift by hand so I opened it, had a look, all normal, put it back together & it worked, may have been a crippled over spring. Funny thing is that it wasnt a problem or noticeable, maybe there's something in that, I'll get into the diaphram system & check all is ok there, maybe they just arent lifting the needles & hence the lack of fuel. Maybe I've deleted some tubes I shouldn't have.
There'll be a big discussion at lunch today with dad.
Still like to hear any thoughts, & thanks again for the input.
This is a great club, were doing a GSXR as well & there's no discussion forum for them like this one.
Regards Mitchell
Looking forward to the quiet life !
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Re: 94 zxr750 Won't rev

Postby hipstir70 » Sun May 12, 2013 1:48 pm

Mitchell, i don't if it's the same with the 94 as the 96 but when you took off the anti pollution crap there's two lines that run between no's 1,2 and3,4 from the carburators to the air box do you still have these connected? They need this to balance airbox float bowl pressure. Hope it's simple :D
Rob.
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Re: 94 zxr750 Won't rev

Postby willrcr15 » Sun May 12, 2013 7:04 pm

I think they must be a different setup, the only link between the carbs is the ventilation tubes from the bowls, I think that's what they are. I had a rubber stopper in the end of the plastic tube but have since removed it. did the same thing with the GSXR & it made the carbs flood, as soon as we removed the plug it stopped. Must have had a pressure build up in the bowls above the fuel level & stopped the floats from rising enough to shut off.
We had the big discussion today at lunch but haven't really come up with anything hopeful apart from checking the diaphragms, which are like new condition.
Am I right to think the air above the diaphragm is sucked out & lifts the slide & needle? I haven't checked the vacuum passage but I will. Is that little tab where the suction comes from? The slides do lift when its revved & she revs all good on the stand just not when its ridden.
I'm 105kg, maybe she's telling me something !
We discussed the horrible idea that it may be electrical / Ignitor, is that the ECU ? Does anyone know if they play up or wear out or go bad? It'd be nice to try a known good one then that could be eliminated off the growing list of possibilities.
Dads a good trouble shooter & the problem is clearly something common to all carbs.
I did suspect contaminated fuel from the rust converter I used not being all flushed out but it turned out to be 3rd & 4th leads swapped over DOH ! But that was about 3 tanks of fuel down the drain ago.
Its got to be something simple. I'm thinking about putting all the pollution gear back on & see what happens then work back from there. We sealed off the tappet cover reed valve system with a aluminium plate & gaskets, does anyone know if they're critical or just some bullshit pollution obstacle? Seems they went to a lot of trouble but it all just blows back into the air-box & contaminates the clean new fuel air induction.
Regards Mitchell
Looking forward to the quiet life !
2 Honda NSR 150 SP's for the kids
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97 Suz GSXR750
95 RGV250
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Re: 94 zxr750 Won't rev

Postby JimZXR » Sun May 12, 2013 9:12 pm

From memory I think you have to get the carbs tuned when you take that gear off.
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Re: 94 zxr750 Won't rev

Postby greenman43 » Sun May 12, 2013 9:55 pm

RE. the pollution gear removal, you need to vent the carb breather to the aribox, or it won't run properly at high speed.

Cheers,
Brian
Last edited by greenman43 on Mon May 13, 2013 8:07 pm, edited 1 time in total.
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Re: 94 zxr750 Won't rev

Postby hipstir70 » Mon May 13, 2013 11:33 am

Mitchell, i have some 96 carbs check photo out to see the hoses I'm talking about.
Cheers Rob.
Last edited by hipstir70 on Mon May 13, 2013 11:52 am, edited 2 times in total.
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Re: 94 zxr750 Won't rev

Postby hipstir70 » Mon May 13, 2013 11:37 am

Mitchell, can you see the hoses that come from the top these carbuators are the ones needed to run to airbox.
Cheers Rob.
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07 ZX10r everyday bike
96 ZX7r
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89 ZXR750
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80 Kz750 in build gixxer front & rear end.
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Re: 94 zxr750 Won't rev

Postby willrcr15 » Mon May 13, 2013 12:09 pm

Looks like the same sort of thing.
There must be some suction through the vent tube to all the bowls from the airbox for what reason i dont know. The tube on mine is a single tapered tube, i guess the taper keeps the pressure the same along the line. But doesnt the plenum/air box pressureize ? Anywai ill connect the hose up tonight & try it
Looking forward to the quiet life !
2 Honda NSR 150 SP's for the kids
94 ZX750R
97 Suz GSXR750
95 RGV250
90 FZR 250
81 XS1100
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Re: 94 zxr750 Won't rev

Postby ajverma » Mon May 13, 2013 11:58 pm

hipstir70 wrote:Mitchell, can you see the hoses that come from the top these carbuators are the ones needed to run to airbox.
Cheers Rob.



+1, I put upper engine cleaner through that hose and it feeds straight down the carbs into the engine, and if I didn't keep the revs up, the bike would slowly cut out like it's run out of fuel, and would rev like shit. I had exactly the same problem you have. I realised I had connected that to the airbox, but connected it to the little knob for it which has no hole for it to breathe! (There are two knobs right next to each other and I was in a hurry.. DOH)

That caused the problems you're talking about. They're vacuum lines.
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Re: 94 zxr750 Won't rev

Postby willrcr15 » Tue May 14, 2013 10:43 am

Thanks Rob,
The mysterious world of carbies is something special ! No point trying to understand them just accept the outcome & ask no questions.
I'll try re connecting the vent / vacuum tubes, maybe tonight, couldn't do it last night, bloody work getting in the way again.
Are there any other aftermarket bolt on carbies for my model considering it's for weekend road riding pleasure
Regards Mitchell
Looking forward to the quiet life !
2 Honda NSR 150 SP's for the kids
94 ZX750R
97 Suz GSXR750
95 RGV250
90 FZR 250
81 XS1100
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Re: 94 zxr750 Won't rev

Postby JimZXR » Tue May 14, 2013 12:33 pm

A set off the R model but think they'll set you back a fair bit!
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